Study On The Remaining Oil Distribution And Gradual Profile Control Technology Of Heterogeneous Reservoir

Development of heterogeneous reservoir is in a high water cut stage and the water cut of production wells is rising sharply.The water transports along the strong flooded layer which forming a flow channel advantages.Aimed at the development status of heterogeneous reservoir,the formation mechanism of remaining oil is indicated by studying the microscopic pore structure characteristics.A new method for classifying remaining oil types based on flooding degree was proposed.The distribution of remaining oil after water flooding was described quantitatively according to the water saturation model of Buckley-Leverett and electrode method.In order to exploit the different types of residual oil in the heterogeneous model,a multi-stage flooding technique was adopted to improve oil recovery.The application of polymer in heterogeneous reservoir was determined by the flow test of polymer in core.A multistage plugging and profile control flooding model were presented as progressive flooding method.Through the evaluation of the performance of the oil displacement agent and plugging agent to select the best chemical agents at all levels of slug.The distribution law of remaining oil and the development effect of gradual profile control technology were evaluated by electrode method.Comprehensive use of conventional mercury,controlled mercury,cast thin section and scanning electron microscopy techniques to characterize the distribution of micropore structure in heterogeneous reservoir of Daqing Oilfield.The experimental results show that: with the increase of core permeability,the average pore throat radius increases,the distribution of reservoir pore throat tends to be uniform,the degree of pore bypass is reduced,the pore throat connectivity becomes better and the migration ability of fluid in reservoir becomes stronger.Under the same injection pressure,the oil droplets are more easily and quickly to pass through the capillary with large throat radius.So the distribution of pore structure is the most important reason for the formation of remaining oil.The remaining oil in the heterogeneity reservoir is divided into four types: unswept,spread is not sufficient,wash oil is not sufficient and strong water washable.According to Buckley-Leverett water saturation model and electrode method,the remaining oil in heterogeneous model was descripted qualitatively and quantitatively.The results show that: the recovery rate reached 51% in the in intensity flooded layer and the residual oil is close to the residual oil saturation.The recovery rate is only 6.7% in unwashed layer and a large number of crude oil enrichment in this layer.Displacement experiment result of two parallel models shows that: the key factor to improve the recovery efficiency is to strengthen the effect of swept volume when the strong flooded layer is combined with non flooded layer.The key factor to improve the recovery rate is enhanced the effect of both the swept volume and wash oil when the medium flooded layer is combined with non flooded layer.The key factor to improve the recovery efficiency is to strengthen the ability of washing oil when the weak flooded layer is combined with non flooded layer.In order to improve the oil recovery in heterogeneous reservoir,first plugging water flooding layer,then adjust the input profile,finally strengthening oil displacement system oil capacity.According to the distribution of the remaining oil in heterogeneous reservoir,a multi-stage flooding slug combination method was put forward.The mobility test results show that: the HPAM with a relative molecular mass of 3500×104 was not effective plugging water flooded layer.Therefore,it is necessary to develop a powerful flooding system for strong flooding,the system was preferred to apply to blocking the strong flooded layer which consists of 3000mg/L polyacrylamide AISH1 and 1000mg/L chromium acetate and 100mg/L thiourea.Due to the gel degree of 11021 mPa·s and the gel time of 7 days,the gel system can effectively block the water flooding layer in heterogeneous reservoir.At the same polymer concentration conditions,the viscosity increases with the increasing of molecular weight.The HPAM with relative molecular mass of 2500×10⁴ is selected as the second plug to adjust the water injection profile.Interfacial tension of the SP system which is composed by 1900×10⁴ polyacrylamide and sulphobetaine surfactants compound system can reach 10^-3 magnitude.Therefore,the system can be improved the micro oil displacement efficiency in water-flooded layer and weak-flooded and non-flooded layer.The mount of each stage was optimizated by heterogeneous cores,the best test can be enhanced oil recovery 19.7%.Using the electrode method to measure oil saturation,it can intuitively describe the variation of the residual oil saturation in the intuitive and vertical heterogeneity model.The experimental results show that multi slug combination has a good effect on starting the residual oil in heterogeneous reservoir.The research results of this paper have an important guiding role for further measures of heterogeneous reservoir after polymer flooding.